Existing 802 technology (802.11 WLANs, 802.15 wireless personal area networks (WPANs), etc.) traditionally does not have to support emergency calls like cellular does. For cellular, support of emergency calls often resulted from regulatory requirements imposed on the technology and is therefore widely implemented in most of today's deployed wireless cellular networks and handsets. Support for emergency calls involves many aspects across all communication layers, especially signaling support and mandated procedures, which are non-existent for 802.11 and 802.15 technologies. With the advent of voice over Internet Protocol (VoIP) in WLANs and increased everyday usage of WLANs, support for emergency calls in WLANs will become necessary.
Even “fixed” VoIP phone service offerings for the residential market have limited emergency call support. Number location information cannot always be tracked by a dispatcher in a public safety answering point (PSAP), call back is not always possible, and address registration may be required upon purchase of the equipment. When the VoIP phone is moved to a new location, the emergency call will still be sent based on the registered address location. The registered address can be changed in principle, but delays are at least on the order of days or weeks in updating the information at the PSAP. In addition, some users might not update their registration information in a timely manner, if at all.
This situation worsens with more mobility as enabled by VoIP phones using WLANs. WLAN based VoIP phones can work from any location and the user can be expected to roam seamlessly between locations, such as from an office to a home to public hotspots, etc.
Certain 802.11-specific issues exist, including radio access, access point (AP) location, caller location, and emergency call admission. In regard to radio access, no priorities for emergency calls currently exist in the 802.11 standards, and there is no means to distinguish an emergency call from a regular call for the WLAN access network. The location of an AP or a STA is currently unknown to the network in a non-proprietary manner, even if for example, the AP's identification can easily be determined. It is also not currently possible to map the caller's location in a non-proprietary manner.
In regard to admission, a tightly managed WLAN may prevent emergency callers from establishing an emergency call if the caller is not authorized to enter the network. The normal connection procedure between a STA and an AP requires the STA to send an Association request, followed by negotiation with the AP prior to associating the STA to the AP. If the STA is unable to indicate that it is making an emergency call, it would have to go through the entire association procedure to determine if it could be admitted. As an example of this type of difficulty, if a STA does not have the proper password or authentication credentials to access the system (if the AP is configured to require passwords or require authentication credentials, as might exist for example with a private hotspot or enterprise/office WLAN), the AP will bluntly refuse the STA's association request. But even if the STA has the proper password or authentication credentials, the AP could still refuse admittance to the network based on its configured maximum capacity for voice users. In this case, the right decision for the AP would be to admit this new emergency call (at the highest priority) and to discontinue another existing voice call. Because the AP currently lacks means to make this distinction in the first place, such a feature cannot be implemented with existing state-of-the-art WLAN technology. Contrast this with the operation of a cellular system, in which any device can make an emergency call, even a device without a SIM card.